Right crank arm assembly for a bicycle and crank arm thereof

ABSTRACT

A right crank arm assembly for a bicycle, comprises a right crank arm, a first annular element directly coupled with said crank arm at least one first coupling portion of said first annular element and at least one second annular element coupled with said crank arm and of a smaller size than said first annular element. The first annular element comprises a toothing that extends radially towards the outside along a primitive circumference having a predetermined diameter. Said at least one first coupling portion is entirely contained in a first area extending radially towards the outside starting from an ideal circumference having a diameter at least equal to ⅔ of said predetermined diameter. Such an annular element constitutes the front sprocket of the crank arm assembly of the present invention and consists of a simple toothed band. Such a front sprocket is particularly light in weight.

FIELD OF INVENTION

The present invention relates to a right crank arm assembly and rightcrank arm for a bicycle.

BACKGROUND

Typically, in the field of bicycles, the expression “right crank armassembly” is used to indicate an assembly comprising a right crank armand at least one front sprocket coupled with the right crank arm. Thefront sprocket, in particular, is the toothed wheel adapted to drive thechain of the bicycle for the motion transmission to the rear wheel ofthe bicycle, such motion being imparted by the cyclist through pedaling.

Right crank arm assemblies are known in which the front sprocket isdirectly coupled with the right crank arm.

Right crank arm assemblies are also known in which the front sprocket iscoupled with the right crank arm through the interposition of an adapterdisc made of a light material.

The present invention relates in particular to a right crank armassembly in which the front sprocket is directly coupled with the rightcrank arm. In particular, this kind of right crank arm assemblies areheavier than those comprising an adapter, which is a drawback for aprofessional use.

SUMMARY

The present assembly refers, in a first aspect thereof, to a right crankarm assembly for a bicycle, comprising a right crank arm, a firstannular element directly coupled with said crank arm at least one firstcoupling portion of said first annular element and at least one secondannular element coupled with said crank arm and of a smaller size thansaid first annular element, wherein said first annular element comprisesa toothing that extends radially towards the outside along a primitivecircumference having a predetermined diameter, wherein said at least onefirst coupling portion is entirely contained in a first area extendingradially towards the outside starting from an ideal circumference havinga diameter at least equal to ⅔ of said predetermined diameter.

Advantageously, in the assembly, the annular element, which acts as abig front sprocket, has a simple toothed band possibly provided withcoupling elements with the crank arm having a very short radialextension. In this way a substantial saving in weight of the elementthat constitutes the big front sprocket and, therefore, of the rightcrank arm assembly is obtained. Such a saving in weight is particularlysignificant in the case in which the crank arm is made from lightmetallic material or, preferably, from composite material.

BRIEF DESCRIPTION OF THE DRAWING(S)

Further characteristics and advantages described herein shall becomeclearer from the following detailed description of some preferredembodiments thereof, made with reference to the attached drawings. Insuch drawings:

FIG. 1 is a front view from the inner side of a right crank arm assemblyaccording to the present invention, comprising a combination of standardfront sprockets;

FIG. 2 is a front view of the outer side of the assembly of FIG. 1;

FIG. 3 is a front view of the inner side of a right crank arm assemblyaccording to the present invention, comprising a combination ofcompact-type front sprockets;

FIG. 4 is a front view of the outer side of the assembly of FIG. 3;

FIG. 5 is a section view according to the section line V-V of FIG. 3;

FIGS. 6 to 8 are respectively a perspective view, a view of the innerside and a view of the outer side of a right crank arm according to thepresent invention, such a crank arm being used in the assembly of FIG.1;

FIG. 9 is an enlarged section view according to the line IX-IX of FIG.7;

FIGS. 10 and 11 are respectively perspective views of the inner side andof the outer side of a front sprocket according to the presentinvention, such a front sprocket being used in the assembly of FIG. 1;

FIG. 12 shows a mounting step of the front sprocket of FIGS. 10 and 11onto the crank arm of FIGS. 6 to 8;

FIG. 13 is a front view of the outer side of an alternative embodimentof the crank arm described herein;

FIG. 14 is a perspective view of the inner side of an alternativeembodiment of the front sprocket described herein;

FIGS. 15 and 16 are respectively a front view of the outer side and aperspective view sectioned according to the line XVI-XVI of FIG. 15, ofan alternative embodiment of a right crank arm assembly according to thepresent invention;

FIG. 17 is a front view of the outer side of a further embodiment of aright crank arm assembly according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Introduction

Throughout the present description and in the subsequent claimsindistinct use shall be made of the expression “annular element” or“toothed band” or “front sprocket” to indicate the component of theassembly described herein that in the right crank arm assemblies of theprior art corresponds to the toothed front sprocket.

Preferably, the aforementioned ideal circumference has a diameter atleast equal to ¾ of said predetermined diameter, more preferably atleast equal to ⅘ of said predetermined diameter, more preferably atleast equal to ⅚ of said predetermined diameter, more preferably atleast equal to 6/7 of said predetermined diameter. In this way thedesired lightening in weight of the annular element that constitutes thebig front sprocket is obtained, at the same time ensuring a goodcoupling between annular element and crank arm.

In a first embodiment of the assembly described herein, said at leastone first coupling portion is defined by at least one first couplingelement that extends radially cantilevered from a radially inner surfaceof the first annular element up to said ideal circumference.

In this embodiment, preferably, said first annular element comprises atleast one first contact element with the crank arm which is structurallydistinct from said at least one first coupling element, said at leastone first contact element also extending and being entirely contained inthe aforementioned area.

Advantageously, the provision in the annular element of contact elementswhich are structurally distinct from the coupling elements allows acontact of the annular element on the crank arm to be achieved that ismore stable and effective than what occurs in assemblies of the priorart, where the contact between front sprocket and crank arm only occursat the coupling elements of the front sprocket with the crank arm. Inthis way it is possible to limit the deformation of the annular elementduring pedaling, with a consequent advantage in terms of motiontransmission. Even more advantageously, these contact elements also havea limited radial extension, thus contributing to the lowering of theweight of the annular element and, therefore, of the assembly describedherein.

More preferably, said at least one first contact element extends fromsaid radially inner surface to an angular position of said first annularelement different to that of said at least one first coupling element.

Preferably, said at least one first contact element extends along anon-radial direction with respect to a rotation axis of said firstannular element. Advantageously, unlike assemblies of the prior artwhere the contact between front sprocket and crank arm only occurs atthe ends of the arms of the crank arm and of the coupling elementsextending radially with respect to the rotation axis of the assembly, inthe assembly described herein the contact between annular element andcrank arm occurs at respective surfaces having a greater extension. Thedesired stability and effectiveness of the contact is thus ensured.

More preferably, said at least one first contact element extends atleast partially circumferentially around said rotation axis along an arcof circumference having a predetermined angular extension.

In a first embodiment of the annular element of the right crank armassembly described herein, said angular extension is equal to 360°.

In a second embodiment of the annular element of the right crank armassembly described herein, said angular extension is less than 360° andpreferably more than 15°, more preferably between 15° and 100°, evenmore preferably between 30° and 75°.

In the preferred embodiment of the right crank arm assembly describedherein, said first annular element comprises a plurality of firstcoupling elements and said at least one first contact element extendscircumferentially without structural interruption between two adjacentcoupling elements of said plurality of first coupling elements.

In the assembly described herein, the crank arm has an inner sideintended, in use, to face towards the frame of the bicycle and an outerside opposite said inner side and said at least one first contactelement is preferably active on said crank arm on one of said sides.

Preferably, said annular element also comprises at least one secondcontact element active on said crank arm on the other of said sides.

Advantageously, the provision in the annular element of elements adaptedto act in contact with the two opposite sides of the crank armeffectively blocks the twisting deformation of the annular elementduring pedaling, to the great advantage of the transmission efficiencyof the motion imparted through the right crank arm assembly describedherein. The Applicant has indeed observed that, in operation,conventional front sprockets elastically deform due to the stresses towhich they are subjected during pedaling. Such a deformation leads to adecrease in transmission efficiency of the motion imparted through thecrank arm assembly. In particular, the crank arm transmits the forcethat the cyclist exerts upon the pedals of the bicycle to the frontsprocket. Such a force acts in a plane parallel to the middle plane ofthe front sprocket and its direction of application and the intensitychange at each angular position of the pedal. This stress thereforecauses a variable lateral flexing deformation of the front sprocket.Considering also that the chain exerts a force resisting the forwardmovement of the front sprocket on a portion of the front sprocket, theresulting stress on the front sprocket is a twisting stress. Therefore,the consequent deformation of the front sprocket is a twistingdeformation. The Applicant has also found that, during pedaling, thefront sprocket twists on different sides from one point to another, andtherefore has thought to position contact elements with the crank arm atboth sides of the crank arm.

Preferably, said at least one second contact element extendscantilevered from said radially inner surface of said first annularelement on the opposite side to said at least one first contact elementwith respect to said at least one first coupling element.

The Applicant has indeed found that the front sprocket of conventionalassemblies twists on opposite sides before and after each couplingelement with the crank arm, and has therefore thought to position thecontact elements on the opposite side to each coupling element. Inparticular, the contact elements are only positioned where they actuallyperform their counteraction to the twisting deformation of the annularelement, i.e. just at the side of the annular element in which it twistsduring pedaling. In this way a substantially saving of weight isobtained in addition to an excellent result in terms of prevention oftwisting deformation of the annular element.

Preferably, said at least one second contact element extends from saidradially inner surface of said first annular element along asubstantially radial direction.

In the preferred embodiment of the front sprocket of the right crank armassembly described herein, said at least one second contact element isarranged in a position that precedes said at least one first couplingportion with reference to the direction of rotation of the crank armassembly during pedaling and said at least one first contact element isarranged in a position that follows said at least one first couplingportion with reference to said direction of rotation. The Applicant hasindeed found that such a geometry provides an effective opposition tothe deformation of the annular element during pedaling.

In a first embodiment of the assembly described herein, said at leastone first contact element and at least one second contact element aredefined in a body portion of said first annular element extendingradially cantilevered from said radially inner surface and comprisingsaid at least one first coupling element.

In a second embodiment of the assembly described herein, said at leastone second contact element is defined by a respective body portion ofsaid first annular element extending radially cantilevered from saidradially inner surface, said respective body portion not comprising saidat least one first coupling element.

Preferably, said first annular element comprises at least one abutmentsurface adapted to allow the correct angular positioning of said crankarm with respect to said first annular element.

More preferably, said at least one abutment surface is defined at leastpartially in said at least one second contact element. Advantageously,it is in this way possible to achieve the correct angular positioning ofthe crank arm with respect to the annular element without needing toprovide special abutment elements on the annular element.

In the preferred embodiment thereof, the annular element of the assemblydescribed herein comprises a plurality of first contact elements and aplurality of second contact elements. In particular, the contactelements are preferably at least two per side, possibly four, but thisdoes not exclude embodiment with a different, even odd, number ofcontact elements. Advantageously, the provision of many contact elementsper side allows a contact between crank arm and annular element to beobtained that is particularly stable and effective in blocking thetwisting deformation of the annular element.

Preferably, the assembly described herein further comprises at least onefirst crank arm element adapted to cooperate with said at least onefirst contact element and at least one second crank arm element adaptedto cooperate with said at least one second contact element.

Preferably, said at least one first crank arm element has an angularextension substantially equal to that of said at least one first contactelement.

In a specific embodiment thereof, said first annular element is coupledwith said crank arm at least one first coupling portion of said crankarm and said at least one second annular element is coupled with saidcrank arm at least one second coupling portion of said crank armdifferent to said first coupling portion. Advantageously, the provisionon the crank arm of different coupling portions for the differentannular elements makes the removal of the annular elements for possiblerepairs or replacement quicker and easier. This cannot be achieved inassemblies of the prior art wherein all of the front sprockets arecoupled with the crank arms at the same coupling portions of the crankarm.

Preferably, said at least one first coupling portion of said crank armis defined at a first circumference having its centre at the rotationaxis of said crank arm and said at least one second coupling portion ofsaid crank arm is defined at least one second circumference concentricto said first circumference and having a different diameter to that ofsaid first circumference. Advantageously, the provision of annularelements of different diameter coupled with different coupling portionsof the crank arm allows a large number of combinations of annularelements of different size to be made, such combinations also comprisingannular elements of very small or very large diameter. Regarding this,it should be noted that, in conventional assemblies, the onlycombinations used are those known as “standard”, comprising small frontsprockets with a number of teeth of between 38 and 44 and large frontsprockets with a number of teeth of between 52 and 56, and “compact”,comprising small front sprockets with a number of teeth of between 32and 36 and large front sprockets with a number of teeth of between 46and 50. The assembly described herein, on the other hand, allowsdifferent combinations to “standard” or “compact” to be adopted, likefor example mixed combinations.

The Applicant has also found that, in conventional crank arms, the armsare sized to give the maximum resistance to twisting in combination withfront sprockets of predetermined size. The result of this is that, inthe case in which the cyclist intends to use front sprockets ofdifferent sizes and wants to maintain an acceptable structural rigidity,he is forced to replace also the right crank arm. This, as well asconstituting a trouble for the cyclist, implies that the crank armmanufacturer needs to design, produce and commercialize crank arms ofdifferent sizes.

Advantageously, with an assembly like the one described herein in whichannular elements of different diameter are coupled at different couplingportions of the crank arm, it is no longer necessary to producedifferent sized crank arm for each combination of annular elementsintended to be used, nor does the cyclist have to change crank arm eachtime he changes the combination of annular elements in order to be ableto maintain the desired structural rigidity. The assembly is thereforeadvantageous both for the cyclist and for the crank arm manufacturer.

More preferably, said at least one first coupling portion of said crankarm is defined along at least one first substantially radial directionwith respect to said rotation axis of the crank arm and said at leastone second coupling portion of said crank arm is defined along at leastone second substantially radial direction of said crank arm different tosaid first substantially radial direction of said crank arm.

Preferably, said crank arm comprises at least two first couplingportions arranged at a first predetermined angular distance one from theother and at least two second coupling portions arranged at a secondpredetermined angular distance one from the other, said secondpredetermined angular distance being less than said first predeterminedangular distance.

Preferably, said first area is a first annular area located between saidideal circumference and a second ideal circumference arranged at least 1mm radially towards the inside with respect to said toothing.

More preferably, said first annular area has an inner diameter greaterthan or equal to 150 mm and an outer diameter less than or equal to 180mm. Even more preferably, said first annular area has an inner diametergreater than or equal to 160 mm and an outer diameter less than or equalto 170.

Preferably, the assembly described herein comprises a second annulararea containing said at least one second coupling portion of said crankarm and having an inner diameter greater than or equal to 100 mm and anouter diameter less than or equal to 130 mm.

Preferably, said second annular area has an inner diameter greater thanor equal to 110 mm and an outer diameter less than or equal to 120 mm.

In a variant of the assembly described herein, the aforementioned atleast one coupling portion is defined by said radially inner surface. Inthis case, preferably, the aforementioned radially inner surface isarranged at least 1 mm radially towards the inside with respect to saidtoothing.

Preferably, said coupling portion comprises at least one surface portionextending radially and/or at least one surface cylindrical portionextending around a rotation axis of said assembly.

Preferably, in the preferred embodiments of the assembly describedherein the crank arm comprises an arm of predetermined length L and aplurality of coupling arms with said first annular element extendingsubstantially radially with respect to a rotation axis of the crank armand the radial extension of which is defined by a circumference ofdiameter T″, in which L/T″ is between 0.7 and 1.

Preferably, the ratio L/T″ is between 0.8 and 0.9.

Preferably, in the preferred embodiments of the assembly describedherein the crank arm is made from a light metallic material or, morepreferably, from a composite material.

In a second aspect thereof, the present invention relates to a rightcrank arm for a bicycle, comprising an arm of predetermined length L anda plurality of coupling arms with a toothed annular element extendingsubstantially radially with respect to a rotation axis of said crankarm, wherein the radial extension of said coupling arms is defined by anideal circumference of diameter T″, wherein the ratio L/T″ is between0.7 and 1.

Advantageously, such a crank arm can be used in an assembly of the typedescribed above. In particular, since such a crank arm has longer armsthan those of crank arms of the prior art, it can be coupled both withan annular element having coupling portions with the crank arm extendingcantilevered from the radially inner surface of the annular element andof short radial extension, and with an annular element in which thecoupling portions are defined by the same radially inner surface of theannular element.

Preferably, the ratio L/T″ is between 0.8 and 0.9.

Preferably, the crank arm described herein comprises first couplingportions with the annular element arranged on the coupling arms at afirst annular area having an inner diameter greater than or equal to 150mm and an outer diameter less than or equal to 180 mm.

More preferably, said first annular area has an inner diameter greaterthan or equal to 160 mm and an outer diameter less than or equal to 170mm.

Preferably, the crank arm described herein further comprises secondcoupling portions with a second annular element arranged on the couplingarms at a second annular area having an inner diameter greater than orequal to 100 mm and an outer diameter less than or equal to 130 mm.

More preferably, said second annular area has an inner diameter greaterthan or equal to 110 mm and an outer diameter less than or equal to 120mm.

In the preferred embodiment of the crank arm described herein, saidcoupling portions comprise threaded holes.

DESCRIPTION

With reference to FIGS. 1 and 2, a first embodiment of a right crank armassembly according to the present invention is indicated with 1. Theassembly 1 comprises a right crank arm 5, a front sprocket of largerdiameter 10 (hereafter indicated as big front sprocket) and a frontsprocket of smaller diameter 15 (hereafter indicated as small frontsprocket). Alternative and not illustrated embodiments are foreseen inwhich the assembly 1 comprises just one front sprocket, for example foruse on a racing track, or more than two front sprockets, for examplethree.

Throughout the present description and in the subsequent claims, the“inner side” of the assembly 1, of the crank arm 5 and/or of the frontsprockets 10 and 15 shall indicate the side visible in FIGS. 1 and 3,i.e. the one facing towards the frame of the bicycle when the assembly 1is mounted in the bottom bracket assembly. On the other hand “outerside” shall indicate the side opposite the inner side, visible in FIGS.2 and 4.

Throughout the present description and in the subsequent claims,moreover, “previous position” or “following position” shall respectivelyindicate the position of an element that precedes and that follows areference element in the direction of rotation of the crank arm, wherethe rotation is in the direction such as to transmit driving force tothe rear wheel.

The right crank arm 5 described herein can be made from metallicmaterial, like a light alloy, such as aluminum or magnesium and theiralloys, or from composite material, comprising structural fibersincorporated in a polymeric material. Typically, the structural fibersare selected from the group consisting of carbon fibers, glass fibers,aramid fibers, ceramic fibers, boron fibers and combinations thereof,carbon fibers being preferred. Preferably, the polymeric material of thebody of the component is thermosetting. However, the possibility ofusing a thermoplastic material is not excluded. More preferably, thepolymeric material comprises an epoxy resin. While these materials arepreferred, they are not limiting to other materials that may be chosen.

The arrangement of said structural fibers in the polymeric material canbe a random arrangement of pieces or sheets of structural fibers, asubstantially unidirectional ordered arrangement of fibers, asubstantially bidirectional ordered arrangement of fibers, or acombination of the above.

In an alternative embodiment, the fibers are organized in a fabric woundwith continuity around a recess, as described in patent EP 1270394 andin European patent applications no 06425086 and 06425087 (U.S.application Ser. Nos. 11/657,279 and 11/501,565) to the same Applicant,the content of which are incorporated herein by reference as if fullyset forth.

With particular reference to FIGS. 6 to 8, the right crank arm 5comprises an main body 20 having a first end 21 for coupling with apedal (not illustrated) and a second end 22 for coupling with the frontsprockets 10 and 15 and with a shaft of a bottom bracket assembly (notillustrated). In particular, the second end 22 comprises a hole 23 forhousing the shaft of the bottom bracket assembly. In alternative and notillustrated embodiments but known to a person of ordinary skill in theart, the shaft is removably coupled with the right crank arm, or it isan integral part thereof.

A support structure 25 of the front sprockets 10 and 15 is providedabout the hole 23, comprising four coupling arms (or spokes) 27 thatextend substantially radially around the hole 23 inside of which arotational axis X of the crank arm 5 is defined.

At the respective free end portions 28 the arms 27 are connected in setsof two by a reinforcing element 30, preferably extendingcircumferentially around the rotational axis X of the crank arm 5 andmade in the form of an arc of circle.

Each reinforcing element 30 that connects a pair of arms 27 comprises acontact surface 32 at the outer side of the big front sprocket 10.

The contact surfaces 32 preferably have an angular extension α (FIG. 7)greater than or equal to 15°, preferably between 15° and 100°, morepreferably between 30° and 75° and are arranged at an angular distance βfrom the middle plane Π of the elongated body 20, where β is preferablybetween 30° and 90°.

In an alternative embodiment of the crank arm 5 (not illustrated) thepairs of arms 27 connected by the element 30 are replaced by a singlearm of equal angular extension.

Now considering the pairs of arms 27 connected together by the element30, the arm 27 of each of them coming first in the direction of rotationω of the right crank arm 5 around the rotational axis X of the crank arm5, comprises an element 35 extending cantilevered in the circumferentialdirection in the direction of rotation ω. Each element 35 comprises acontact surface 40 at the inner side of the big front sprocket 10.

Coupling portions 44 with the big front sprocket 10 are defined at thefree ends 28 of each arm 27. The element 30 connects the coupling arms27 right at such coupling portions 44. The coupling portions 44 areprovided with coupling holes 45.

The coupling portions 44 with the ends 28 of the arms 27 connected bythe element 30 are arranged at an angular distance Y from each other ofbetween 45° and 95°, and the coupling portion 44 closest to theelongated body 20 is arranged at an angular distance μ of between 35°and 85° from the plane Π.

An additional coupling hole 46 with the front sprocket 10 is preferablyprovided on a portion of the elongated body 20 (FIG. 7).

The section of FIG. 9 shows in detail an example embodiment of thecoupling portions 44 in the case in which the right crank arm 5 is madefrom composite material. The coupling portions 44 are in this casepreferably defined by metallic inserts 50 provided with a threaded hole52 for the insertion of a screw (not illustrated). The outer surface 54of the inserts 50 is irregular, and preferably threaded, so as to beable to be better held in the composite material, to which it is fixedby gluing or by direct adhesion due to a co-moulding process.

An alternative embodiment of the assembly described herein is foreseenin which the threaded hole 52 is directly made in the compositematerial.

As shown in detail in FIG. 1, the crank arm 5 described herein furthercomprises, in a preferred embodiment thereof, second coupling portions47 used for the coupling of the small front sprocket 15. The couplingportions 47 are preferably made identical to the coupling portions 44and comprise coupling holes 48.

The coupling portions 44 and 47 are at different distances from therotational axis X of the right crank arm 5. In particular, their axes ofsymmetry S1 and S2 lie on two ideal circumferences of differentdiameter.

As illustrated in FIGS. 1, 3, 6, 7 and 12, the coupling portions 44 and47 are preferably non-radially aligned with each other. Indeed, thecoupling portions 44 are at smaller angular distances γ apart than theangular distances between the coupling portions 47.

Both the big front sprocket 10 and the small front sprocket 15 arecoupled with the main body 20 of the crank arm 5 at the additionalcoupling portion 46.

With particular reference now to the section illustrated in FIG. 5, in apreferred embodiment described herein the contact elements 30 and 35respectively at the outer side and at the inner side of the big frontsprocket 10 are located substantially at the opposite side with respectto the coupling portions 44, identified by the axis of symmetry S1 (saidaxis is parallel to the rotational axis x of the crank arm 5). Inparticular, the surface 32 of the element 30 for contact at the outerside of the front sprocket 10 follows the coupling portion 44 in thedirection of rotation ω, whereas the surface 40 of the element 35 forcontact at the inner side of the front sprocket 10 precedes the couplingportion 44 (FIGS. 6 and 7). The elements 30 and 35 are therefore activein abutment on the front sprocket at different angular positions. Itshould be appreciated from FIG. 5 that the first contact element 30 andthe second contact 40 element are offset from one another along therotational axis of the right crank arm 5; this offset creates a gap inwhich the front sprocket 10 is engaged.

In an alternative embodiment of the crank arm illustrated in FIG. 13 andindicated with 5′, the arms 27′ instead of being connected in sets oftwo through the elements 30, each comprise an element 30′ extendingcantilevered circumferentially around the rotational axis X of the crankarm 5′. Each element 30′ comprises a respective contact surface 32′ atthe outer side of the big front sprocket 10. Each of the arms 27′ alsocomprises a respective contact surface 40′ at the inner side of the bigfront sprocket 10. The contact surfaces 32′ and 40′ are arranged in aposition respectively prior to and after the coupling portion 44 (hiddenin the figures) provided on the arm 27. In this case, the number of arms27 can also be odd, for example three or five.

In a further not illustrated embodiment of the assembly describedherein, just one or in any case just a few of the arms 27 comprise acontact surface 40 at the inner side of the big front sprocket 10,between which the arm 27 immediately following the elongated body 20with reference to the direction of rotation ω of the crank arm 5 andpreferably the arm 27 arranged in a substantially symmetrical positionwith respect to the main body 20 of the crank arm 5.

In accordance with the invention, the contact surfaces 32 and 40 do notlie on the same plane, but a predetermined axial distance D apart (FIG.5). In this way the big front sprocket 10 does not need to be deformedto be inserted between the two contact surfaces. It is thus sufficientfor the front sprocket 10 to have a thickness equal to D in the contactarea with the crank arm 5. Preferably D is equal to or less than themaximum thickness of the big front sprocket 10.

In the embodiments illustrated in the attached figures, the elements 30and 35 are integral with the main body 20 of the crank arm 5, but inother not illustrated embodiments such elements can be made in separatepieces and coupled with the crank arm 5.

In FIGS. 10 and 11, the big front sprocket 10 of the right crank armassembly 1 shown in FIGS. 1 and 2 is illustrated.

Such a front sprocket comprises an annular element 11, preferably madefrom light metal alloy or from composite material, having a radiallyouter annular surface 12 on which a toothed portion 100 (hereafter alsoindicated as toothing) is formed extending radially towards the outsideand a radially inner annular surface 13 from which four elements 98 forcoupling with the crank arm extend radially cantilevered. In particular,the elements 98 are adapted to be coupled with the arms 27 of the crankarm 5 by coupling respective coupling portions defined on the elements98 with the coupling portions 44 defined on the arms 27. The couplingtakes place through screws (not illustrated) inserted in holes 64 formedon each coupling element 98.

On outer side thereof (FIG. 11) the big front sprocket 10 comprises twoelements 55 having respective contact surfaces 60 adapted to contact thecontact surfaces 32 of the elements 30 of the right crank arm 5. Theelements 55 have the same angular extension as the elements 30 and eachelement 55 extends without structural interruption between two adjacentelements 98. What has been stated above with reference to the number,angular position with respect to the coupling portions 44 and angularextension of the elements 30 of the crank arm 5 with respect to therotational axis of the crank arm is therefore also valid for theelements 55 of the front sprocket 10 with reference to the couplingportions defined on the elements 98 and with reference to the rotationalaxis of the front sprocket.

The elements 55 are preferably surmounted in the radial direction by athroat 62 extending according to an arc of circle.

At the ends of the elements 55 the holes 64 for the passage of thescrews that insert into the inserts 50 of the right crank arm 5 areformed.

On the inner side of the front sprocket 10 (illustrated in FIG. 10), onthe other hand, a pair of elements 65 are provided having respectivecontact surfaces 66 adapted to contact the contact surfaces 40 of theelements 35 of the right crank arm 5.

The big front sprocket 10 further comprises an additional arm 68 with ahole 69 for the passage of a screw intended to insert into the holeformed in the additional coupling portion 46 of the crank arm 5, in thecase in which such an additional coupling portion is present.

In the embodiment of the big front sprocket 10 illustrated in detail inFIGS. 10 and 11, each contact element 55 and 65 with the crank arm 5 isdefined at a single body portion 14 of the annular element 11 thatextends radially cantilevered towards the centre of the front sprocket10 from inner surface 13 thereof and that also comprises a pair ofcoupling elements 98. The elements 55, 65, and 98 are therefore all anintegral part of the body portion 14.

FIG. 14 shows an alternative embodiment of the big front sprocket,indicated with 10. In such an embodiment no single body portion 14 thatcomprises the elements 65 and 98 can be identified. Indeed, the bodyportion 14 here comprises just the contact element 55 and a pair ofelements 98 for coupling with the crank arm 5, whereas the contactelements 65 with the crank arm are defined at further and respectivebody portions 140, distinct and separate from the body portion 14 of theannular element 11, which also extend radially cantilevered from theinner surface 14 of the annular element 11 towards the centre of thefront sprocket 10 and which do not comprise the coupling elements 98 andthe contact elements 55 with the crank arm 5.

In such an embodiment, the elements 98 and 65 are made adjacent to thetoothed portion 100 of the front sprocket 10. Preferably, consideringthe diameter T of the primitive circumference of the toothed portion100, the elements 98 and 65 are located and entirely contained in anannular area extending radially between the inner surface of saidannular element and an ideal circumference of diameter T′ such thatT>T′≧aT, where a is selected from ⅔, ¾, ⅘, ⅚ or 6/7.

Preferably, the aforementioned inner surface is defined at an idealcircumference arranged at least 1 mm radially towards the inside fromthe toothed portion 100.

The front sprocket 10 in this case therefore reduces to a toothed bandprovided with radial projections constituting the coupling elements 98and the contact elements 55 and 65 and having a short radial extension.Consequently, the maximum radial extension of the coupling arms providedin the crank arm is defined by a circumference of diameter T″ (see FIGS.2 and 4) such that T>T″>T′, where the difference between T and T″ issimply given by the need to leave a free front sprocket portion which issufficient to allow the engagement of the teeth with a chain.

With particular reference to FIG. 4, if L indicates the length of thearm of the crank arm (such a length being commercially set at 170 mm,172.5 mm and 175 mm), the crank arm of the assembly described herein issized so that the ratio L/T″ is between 0.7 and 1, preferably between0.8 and 0.9.

A not illustrated embodiment is foreseen in which the front sprocket hascoupling elements 98 and contact elements 55 and 65 of short extensionas described above with reference to FIG. 14 and all forming part of asingle body portion 14 as described above with reference to FIG. 11.

It should be noted how, in all of the embodiments of the front sprocket10 of the assembly described herein, the contact portions of the frontsprocket 10 with the crank arm 5 are structurally and physicallydistinct from the respective coupling portions.

In the case of use of the front sprocket of FIG. 11 or of the notillustrated embodiment in which the front sprocket has coupling elements98 and contact elements 55 and 65 of short extension as described abovewith reference to FIG. 14 and all forming part of a single body portion14 as described above with reference to FIG. 11, the crank arm of theassembly described herein has coupling arms having a greater radialextension than those of conventional crank arms. In particular, while inconventional crank arms the diameter of the ideal circumference definedby the coupling holes at the big front sprocket and at the small frontsprocket is 130 mm or 135 mm in the case of standard combinations and110 mm in the case of compact combinations, in the crank arm of theassembly described herein the diameter of the ideal circumferencedefined by the holes 45 for coupling with the big front sprocket 10 iswithin an annular area having an inner diameter greater than or equal to150 mm and an outer diameter less than or equal to 180 mm, preferably aninner diameter greater than or equal to 160 mm and an outer diameterless than or equal to 170 mm, whereas that of the ideal circumferencedefined by the holes 48 for coupling with the small front sprocket 15 iswithin an annular area having an inner diameter greater than or equal to100 mm and an outer diameter less than or equal to 130 mm, preferably aninner diameter greater than or equal to 110 mm and an outer diameterless than or equal to 120 mm.

FIGS. 1 and 2 show a right crank arm assembly comprising a combinationof standard front sprockets, i.e. a small front sprocket with a minimumof 39 teeth coupled with a big front sprocket with a number of teeth ofbetween 52 and 56 (53 in the front sprocket 10 illustrated).

However, the right crank arm 5 illustrated in FIGS. 6, 7 and 8 cansupport a wide range of combinations of front sprockets, for example acompact combination, as illustrated in FIGS. 3 and 4, in which the smallfront sprocket 15′ has a minimum number of teeth equal to 34 and the bigfront sprocket 10′ has a number of teeth of between 46 and 50 (48 in thecombination illustrated).

It should however be noted that the right crank arm 5 allows any size offront sprockets to be mounted, for which reason it is also possible toadopt combinations of front sprockets different to the standard andcompact ones, in particular mixed combinations.

As illustrated in FIGS. 6, 7, 8, 13, the crank arm 5, 5′ furthercomprises abutment surfaces 70, 70′ adapted to allow the correct angularpositioning of the crank arm with respect to the front sprocket 10. Suchsurfaces 70, 70′ are defined at a free end of the contact element 35,35′ with the crank arm 5, 5′. Further abutment surfaces 72 are providedat a body portion of the element 35 that extends on the opposite side,with respect to the coupling arm 27, to the one at which the abutmentsurface 70 is defined. The abutment surfaces 70 and 72 cooperate inabutment with corresponding abutment surfaces 74, 76 defined in the bigfront sprocket 10.

FIG. 12 illustrates the way to mount a big front sprocket 10 on a rightcrank arm 5. In particular, the big front sprocket 10 is brought incontact with the right crank arm 5 so that the contact surfaces 32 ofthe elements 30 of the crank arm 5 come into contact with the contactsurfaces 60 of the elements 55 of the front sprocket 10. At this pointthe right crank arm 5 is rotated with respect to the front sprocket 10in the same direction of rotation ω in which it rotates during pedaling.The crank arm 5 shall move with respect to the front sprocket until theabutment surfaces 70 and 72 of the right crank arm 5 make contact withthe corresponding abutment surfaces 74 and 76 of the front sprocket 10.At this point, the contact surfaces 40 of the elements 35 of the crankarm 5 shall be in abutment with the contact surfaces 66 of the elements65 of the front sprocket 10. As a result of this, when the surfaces 74and 76 of the front sprocket 10 are in abutment with the surfaces 70 and72 of the crank arm, the contact surfaces 32, 40, 60 and 66 cooperatewith each other to keep it in position and the operator has both handsfree to fix the screws.

It should be appreciated that the first contact element 55 and thesecond contact element 65 are offset from one another along a rotationalaxis of the annular element 11.

Now with reference to FIGS. 15 and 16, a further embodiment of the rightcrank arm assembly according to the present invention is illustrated,indicated with 200.

The right crank arm assembly 200 comprises a right crank arm 205,preferably made from composite material, comprising a coupling portion210 with an annular toothed band 215. The coupling portion 210preferably comprises an annular-shaped outer peripheral portion 225coupled with the elongated body 220 of the crank arm 205 through aplurality of coupling arms 230.

The coupling between the coupling portion 210 and the toothed band 215can be of any type capable of transmitting torque. In FIG. 16, as anexample, a shape-coupling is illustrated, in particular toothed,preferably strengthened by gluing, or by the adhesion between compositematerial of the coupling portion 210 and the metal of the toothed band215 obtained by co-molding. Alternatively, the toothed band 215 and thecoupling portion 210 could be made with a threading at their interfaceto be screwed (and then possibly glued) one to the other. According to afurther alternative, the toothed band 215 is fixed onto the couplingportion 210 through screws or other fastening elements.

It should be observed that, although FIG. 16 shows a radial couplinginterface 240 and a circumferential coupling interface 245, it does notexclude embodiments in which the coupling is just circumferential orjust radial (in which case there are no front or rear contact surfacesas for the embodiments of FIGS. 1 to 14). The coupling between thetoothed band 205 and the coupling portion 210 could also be a dovetailcoupling, or a coupling extending along a surface inclined with respectto the rotational axis of the annular toothed band 215.

It should also be observed that, although in FIG. 15 just one annulartoothed band 215 is shown, an embodiment is foreseen in which the rightcrank arm 205 is also coupled with a front sprocket or annular band ofsmaller diameter. The coupling between such an annular band of smallerdiameter and the right crank arm 205 is of the same type as thatdescribed with reference to the annular toothed band 215.

As highlighted in the variant 200′ of FIG. 17, the coupling portion210′, instead of being extended according to a complete ring, cancomprise ring portions 225′, for example having the dimensionsillustrated with reference to the support structure 25 of the crank arm5 of FIGS. 6, 7 and 8. The coupling between the coupling portion 210′and the annular toothed band 215′ is of the same type described for theassembly 200 of FIGS. 15 and 16.

FIG. 17 also shows that the right crank arm assembly 200′ (just like theone 200 of FIG. 15) can comprise a second front sprocket or toothed band216 of smaller diameter with respect to the toothed band 215′. The smallfront sprocket 216 can be of the type illustrated with reference to theright crank arm assemblies of FIGS. 1 to 4, or else a toothed bandsimilar to the toothed band 215′, coupled with the crank arm 205′ in thesame way as the toothed band 215′.

In all of the embodiments described and illustrated, the small frontsprocket 15 is coupled with the right crank arm 5 in a conventional way,i.e. contacting just the outer side. However, an embodiment is foreseenin which the coupling between the small front sprocket 15 and the crankarm 5 is the same as that described for the big front sprocket 10, i.e.contacting both the outer side and the inner side.

Numerous variants of the right crank arm 5 are possible, for example theposition of the contact elements at the outer side and at the inner sideof the big front sprocket can be inverted with respect to the couplingportions, thus performing their contact function in different angularpositions of pedaling. The illustrated example is that in which thecontact elements counteract the twisting of the front sprocket in themost critical condition, i.e. when the pedal has passed the vertical tobegin a new descent, since this is the point at which the cyclist exertsthe maximum thrust. The contact surfaces can also face each other andtherefore are at an identical angular position.

What is claimed is:
 1. Right crank arm assembly for a bicycle,comprising a right crank arm having at least two free end portionsspaced away from a rotation axis, an inner side intended, in use, toface towards a frame of the bicycle and an outer side opposite saidinner side, a first annular element having at least one first couplingportion directly coupled with a respective one of said crank arm freeend portions, at least one second annular element coupled with saidcrank arm and of a smaller size than said first annular element, whereinsaid first annular element comprises a toothing that extends radiallytowards the outside along a primitive circumference having apredetermined diameter, wherein said at least one first coupling portionis contained in a first area extending radially towards the outsidestarting from an ideal circumference having a diameter that is less thansaid predetermined diameter, wherein said at least one first couplingportion is defined by at least one first coupling element whichcomprises a hole for coupling with said respective one of said crank armfree end portions, said at least one first coupling element beingentirely formed on a cantilevered portion of said first annular elementand extending-radially inward up to said ideal circumference, whereinsaid first annular element comprises at least one first contact element,that acts on one of said sides of said crank arm, which lacks anycoupling holes and which is structurally distinct from said at least onefirst coupling element, said at least one first contact elementextending radially cantilevered from an inner surface of said firstannular element and being entirely contained in said first area, andwherein said first annular element comprises at least one second contactelement that acts on the other of said sides of said crank arm, said atleast one second contact element extending cantilevered from said innersurface of said first annular element on the opposite side to said atleast one first contact element with respect to said at least one firstcoupling element.
 2. Crank arm assembly according to claim 1, whereinsaid ideal circumference has a diameter at least equal to ¾ of saidpredetermined diameter.
 3. Crank arm assembly according to claim 1,wherein said ideal circumference has a diameter at least equal to ⅘ ofsaid predetermined diameter.
 4. Crank arm assembly according to claim 1,wherein said ideal circumference has a diameter at least equal to ⅚ ofsaid predetermined diameter.
 5. Crank arm assembly according to claim 1,wherein said ideal circumference has a diameter at least equal to 6/7 ofsaid predetermined diameter.
 6. Crank arm assembly according to claim 1,wherein said at least one first contact element extends from said innersurface at an angular position of said first annular element differentto that of said at least one first coupling element.
 7. Crank armassembly according to claim 1, wherein said at least one first contactelement extends along a non-radial direction with respect to arotational axis of said first annular element about which the annularelement rotates.
 8. Crank arm assembly according to claim 7, whereinsaid at least one first contact element extends at least partiallycircumferentially around said rotational axis along an arc ofcircumference having a predetermined angular extension.
 9. Crank armassembly according to claim 8, wherein said angular extension is lessthan 360°.
 10. Crank arm assembly according to claim 9, wherein saidangular extension is greater than 15°.
 11. Crank arm assembly accordingto claim 10, wherein said angular extension is between 15° and 100°. 12.Crank arm assembly according to claim 10, wherein said angular extensionis between 30° and 75°.
 13. Crank arm assembly according to claim 1,wherein said first annular element comprises a plurality of firstcoupling elements and said at least one first contact element extendscircumferentially without structural interruption between two adjacentcoupling elements of said plurality of first coupling elements. 14.Crank arm assembly according to claim 1, wherein said at least onesecond contact element extends from said inner surface of said firstannular element along a substantially radial direction.
 15. Crank armassembly according to claim 1, wherein said at least one second contactelement is arranged in a position that precedes said at least one firstcoupling portion with reference to the counter-clockwise direction ofrotation of the crank arm assembly during pedaling and said at least onefirst contact element is arranged in a position that follows said atleast one first coupling portion with reference to said direction ofrotation.
 16. Crank arm assembly according to claim 1, wherein said atleast one first contact element and at least one second contact elementare defined in a body portion of said first annular element extendingradially cantilevered from said inner surface and comprising said atleast one first coupling element.
 17. Crank arm assembly according toclaim 1, wherein said at least one second contact element is defined bya respective body portion of said first annular element extendingradially cantilevered from said inner surface, said respective bodyportion not comprising said at least one first coupling element. 18.Crank arm assembly according to claim 1, wherein said first annularelement comprises at least one abutment surface that allows correctangular positioning of said crank arm with respect to said first annularelement.
 19. Crank arm assembly according to claim 18, wherein said atleast one abutment surface is defined at least partially in said atleast one second contact element.
 20. Crank arm assembly according toclaim 1, comprising a plurality of first contact elements and aplurality of second contact elements.
 21. Crank arm assembly accordingto claim 1, comprising at least one first crank arm element thatcooperates with said at least one first contact element and at least onesecond crank arm element that cooperates with said at least one secondcontact element.
 22. Crank arm assembly according to claim 21, whereinsaid at least one first crank arm element has an angular extensionsubstantially equal to that of said at least one first contact element.23. Crank arm assembly according to claim 1, wherein said at least onesecond annular element is coupled at at least one second couplingportion of said crank arm different from said at least one firstcoupling portion.
 24. Crank arm assembly according to claim 23, whereinsaid at least one first coupling portion of said crank arm is defined ata first circumference having its center at a rotational axis of saidcrank arm and said at least one second coupling portion of said crankarm is defined at at least one second circumference concentric to saidfirst circumference and having a different diameter to that of saidfirst circumference.
 25. Crank arm assembly according to claim 24,wherein said at least one first coupling portion of said crank arm isdefined along at least one first substantially radial direction withrespect to said rotation axis of the crank arm and said at least onesecond coupling portion of said crank arm is defined along at least onesecond substantially radial direction of said crank arm at a differentradial length to said first substantially radial direction of said crankarm.
 26. Crank arm assembly according to claim 23, wherein said crankarm comprises at least two first coupling portions arranged at a firstpredetermined angular distance one from the other and at least twosecond coupling portions arranged at a second predetermined angulardistance one from the other, said second predetermined angular distancebeing less than said first predetermined angular distance.
 27. Crank armassembly according to claim 1, wherein said first area is a firstannular area located between said ideal circumference and a second idealcircumference arranged at least 1 mm radially towards the inside withrespect to said toothing.
 28. Crank arm assembly according to claim 27,wherein said first annular area has an inner diameter greater than orequal to 150 mm and an outer diameter less than or equal to 180 mm. 29.Crank arm assembly according to claim 28, wherein said first annulararea has an inner diameter greater than or equal to 160 mm and an outerdiameter less than or equal to 170 mm.
 30. Crank arm assembly accordingto claim 27, wherein said at least one second annular element is coupledat at least one second coupling portion of said crank arm different fromsaid at least one first coupling portion, and further comprising asecond annular area containing said at least one second coupling portionof said crank arm and having an inner diameter greater than or equal to100 mm and an outer diameter less than or equal to 130 mm.
 31. Crank armassembly according to claim 30, wherein said second annular area has aninner diameter greater than or equal to 110 mm and an outer diameterless than or equal to 120 mm.
 32. Crank arm assembly according to claim1, wherein said crank arm comprises an arm of predetermined length L anda plurality of coupling arms with said first annular element extendingsubstantially radially with respect to a rotation axis of said crankarm, the radial extension of which is defined by a circumference ofdiameter T″, wherein L/T″ is between 0.7 and
 1. 33. Crank arm assemblyaccording to claim 32, wherein the ratio L/T″ is between 0.8 and 0.9.34. Crank arm assembly according to claim 1, wherein said crank arm ismade from a light metallic material or from a composite material. 35.Right crank arm assembly for a bicycle, comprising a right crank armhaving at least two free end portions spaced away from a rotation axis,a first annular element having at least one first coupling portiondirectly coupled with a respective one of said crank arm free endportions, at least one second annular element coupled with said crankarm and of a smaller size than said first annular element, wherein saidfirst annular element comprises a toothing that extends radially towardsthe outside along a primitive circumference having a predetermineddiameter, wherein said at least one first coupling portion is containedin a first area extending radially towards the outside starting from anideal circumference having a diameter that is less than saidpredetermined diameter, wherein said at least one first coupling portionis defined by at least one first coupling element that is entirelyformed on a cantilevered portion of said first annular element andextends radially inward up to said ideal circumference, and said atleast one first coupling portion is axially separated from said secondannular element, wherein said first annular element comprises at leastone first contact element with said crank arm which is structurallydistinct from said at least one first coupling element, said at leastone first contact element extending radially cantilevered from an innersurface of said first annular element and being entirely contained insaid first area, wherein said crank arm has an inner side intended, inuse, to face towards the frame of the bicycle and an outer side oppositesaid inner side, wherein said at least one first contact element acts onsaid crank arm on one of said sides, wherein said first annular elementcomprises at least one second contact element that acts on said crankarm on the other of said sides, and wherein said at least one secondcontact element extends cantilevered from said inner surface of saidfirst annular element on the opposite side to said at least one firstcontact element with respect to said at least one first couplingelement.